A rope drum is used, for example, in cranes for drawing and storing a hoist rope. In a normal hoisting device, the hoist rope is wound on a rope drum on one or several layers so that the lifted part of the rope is stored on the drum. By winding the rope on more than one layer, the rope drum becomes shorter than when using a rope drum that winds on one layer. A shorter rope drum is naturally more rigid, requires less material and causes less change in the sideward rope angle during winding and, at the same time, reduces the wear of the rope when the sideward movement is reduced, but causes at the same time increased wear of the rope when overlapping layers of the rope are formed. The rope drum may have a rope groove in the form of a spiral where the rope is wound for storage. Due to the single-layered winding, it is also necessary to store and acquire various drums and parts of support for equipment using ropes of different lengths. In multi-layered winding, a longer rope is wound on top of previously wound layers, whereby in the case of a longer rope it is not necessary to change the drum very much. Transmission, instead, either has to be over-dimensioned for equipment using shorter ropes or application-specifically adapted. Namely, when layers increase, the effective radius increases and, accordingly, the transmission ratio between the hoist rope and an engine changes to be more sparsely transmitted. The speed of the rope also changes according to the number of layers on the drum. Thereby, the changing speed of the rope has to be accepted, or the change in the effective radius of the rope drum must be compensated by means of on an engine or gearing. In practice, in even a little more used hoisting devices multi-layer winding is not used, because in a hoisting device of large load, the layers of rope rub against each other and abrade; likewise, the section where the rope rises from one layer to another causes a great strain on the rope. Multi-layer winding is mainly used in mobile cranes by means of which lifting is performed rather rarely, for example, a few times a day.
Instead of a rope drum, a drive wheel has been used in some applications, in the perimeter of which there is one groove for the sideward support of the rope. A number of such drive wheels may be located operationally consecutively so that a desired pulling capacity is achieved. It is not possible to store rope pulled in on a drive wheel. EP 2 185 464 B1 presents an effective solution for the storage of rope pulled in in connection with a drive wheel so that the wound rope does not unnecessarily harm the part of the rope wound on lower layers.
The rope is stretched one percent of its length, for example, depending on the tensile stress. When the rope is wound, the rope slides slightly on the surface of the drive wheel due to the stretching of the rope, and this may cause wear of the rope. Wear is reduced, for example, by lubricating the rope, by using suitably soft lining material on the drive wheel to preserve the rope (e.g. GB 2 254 855 A), or by arranging flexible support between the rope and the drive wheel corresponding to the stretching of the rope in the direction of the perimeter of the drive wheel. Such support that is flexible in the perimeter direction is presented in publications WO 92/09831 A1, US 2006/0022182 A1 and GB 1 508 963.
WO 92/09831 A1 describes a solution where an endless track is formed of intermediate pieces between the drive wheel and the rope, where the intermediate pieces are allowed to slide along the surface of the drive wheel and to prevent the sliding of the rope. In one example in the publication, the drive wheel is simply surrounded by one layer of intermediate pieces joined to each other, which convey the force from the drive wheel to the rope through friction. In another example, an endless chain of intermediate pieces winds two rounds around the drive wheel and a third time for a part of the perimeter of the drive wheel, and then makes a loop under the drive wheel. Thus, it is possible to form contact with a drive wheel through intermediate pieces to the drive wheel at an angle of 720 degrees, i.e. through a length of two rounds. In accordance with this embodiment, the adjacent intermediate pieces slide with regard to both the drive wheel and the adjacent intermediate pieces and the friction that is formed exposes the intermediate pieces to wear and overheating.
US 2006/0022182 A1 describes a winch that is designed to be used with especially valuable synthetic cables or ropes. The examples referred to include electrical and data transfer cables and synthetic ocean exploration ropes that have a small density difference to seawater. The winch has two adjacent drums, which have for each round of the rope a ring formed of elastic material that forms a rope groove forming a full circle. Each ring is allowed to slide on the surface of the drum according to the stretching of the cable. The rings do not form a groove in the form of a spiral for the cable, but the shift from one ring to another is implemented so that, on each ring, the cable is guided for half a round and then the cable is guided to the next ring on the second drum which is half the thickness of the ring further in the axial direction of the drum. Thanks to the two drums, US 2006/0022182 A1 avoids the need to transfer any intermediate pieces outside the drum and the need to create a chain of separate intermediate pieces at all.
GB 1 508 963 describes the pulling equipment of an elevator, which the subsequent US 2006/0022182 A1 resembles. This publication also has two consecutive drums that form tension on a rope through surrounding loops. A groove for the rope is formed by segments that are allowed to move in the direction of the perimeter. The movement in the direction of the perimeter is implemented through flexible radial spools. Thanks to the spools, it is also possible to avoid the problem that the movement in the direction of the perimeter could grow to be unmanageably large if the friction coefficient between the part that slides in the direction of the perimeter and its base were too small—the friction coefficient may not be too large, either, so that the sliding would be implemented and the preservation of the rope could succeed. On the other hand, the publication seems to have common segments or sectors for the adjacent grooves of the rope, which prevents adaptation in the direction of the perimeter in the different grooves in accordance with the stretching of the rope (because the stretching of the rope is not a constant) and exposes the sectors to twisting. The twisting of the sectors may cause a geometrical error that wears the ropes. As in the publication US 2006/0022182 A1, the part of the rope between the drums also hits the edge of the circular grooves at a small angle, because the grooves must be axially slightly to the side from each other.
The aforementioned publications present ways of winding the rope in and out so that the rope angle may stay unchanged and the rope wound in may be stored on a number of layers so that stress does not arise for the layers at the bottom caused by the tension of the rope pulled in. In the publications presented, however, two or more drums or a rope pulley and/or an intermediate piece sliding with regard to the surface pulling in the direction of the perimeter are needed, the management of the friction of which may be difficult. The object of the invention is to avoid or mitigate the disadvantages related to prior art or at least to provide a new technical alternative parallel to prior art.